The field of control valves intended for use within automated process control systems is broad and well known. Many proportional control valves have one or more movable elements that may be actively positioned, anywhere between an extreme open condition and an extreme closed condition, to adjust the flow of fluid passing therethrough. Fluid delivery apparatus intended for manipulating process materials within semiconductor manufacturing equipment usually require attention to the maintenance of high purity of the delivered reactants, and also are typically much smaller than valves used in petrochemical actuators are found in high purity instrumentation and control apparatus, such as mass flow controllers. U.S. Pat. No. 4,695,034 to Shimizu et al. describes the use of a stack of piezoelectric disc elements to effect movement of valve parts in a mass flow controller. U.S. Pat. No. 4,569,504 to Doyle describes the use of a magnetic solenoid with interleaved magnetic circuit elements. U.S. Pat. No. 5,660,207 to Mudd describes the use of a heated resistance wire that changes length with temperature changes in order to effect valve element movement. U.S. Pat. No. 6,178,996 to Suzuki describes the use of a pressurized fluid, such as nitrogen gas, to control the degree of opening of a diaphragm-operated control valve. All of the foregoing patents are herein expressly incorporated by reference, in their entirety.
One important disadvantage of both magnetic solenoid and thermal expansion type actuators is inherent constant power consumption when controlling valve elements positioned at an intermediate condition, such as when actively regulating fluid flow. A piezoelectric actuator is effectively a capacitor in an electrical circuit, and therefore does not consume current when an applied voltage is constant. Consequently, typical piezoelectric control valve applications only require low power and avoid the undesirable generation of heat found in electromagnetic actuators. A piezoelectric actuator advantageously may produce substantially more force than a solenoid actuator of comparable size, but achievable strain severely limits the distance a piezoelectric stack can move. Piezoelectric actuators nearly always are used in a manner wherein applying an activation voltage causes an extensional increase in the stack length (see the Shimizu et al. '034 patent as well as U.S. Pat. No. 5,094,430 to Shirai et al., which is also herein expressly incorporated by reference, in its entirety). Shimizu et al. '034 increases the available movement by interposing a force transmission member, comprising a plurality of radial lever-arm tongues, between the stack of piezoelectric disc elements and the moving portion of the control valve. The Shimizu force transmission members are complicated and difficult to manufacture correctly. Shirai et al. '430 describe the use of a spherical bearing to couple movement from a stack of piezoelectric disc elements to other portions of the control valve to prevent adverse effects otherwise resulting from insufficient parallelism of parts. The use in the Shirai et al. system of a spherical bearing appears to preclude the use of Shimizu's force transmission member. Magnetic solenoid actuators nearly always affect driven element movement analogous to a decrease in length along the actuator axis (see Doyle '504 for example), which is the opposite of piezoelectric actuator behavior. A consequence of these actuator differences is piezoelectric actuators being most likely associated with normally open valves (wherein applying power then causes the valve to decrease fluid flow) and magnetic solenoid actuators being most likely associated with normally closed valves (wherein applying power then causes the valve to increase fluid flow). A valve designer will benefit from having a mechanism to reverse the direction of actuator motion, or change the effective magnitude of actuator motion, to thereby allow both normally open and normally closed valves to use a single actuator type (piezoelectric, magnetic solenoid, pneumatic, etc.).